1. Field of the Invention
The present invention generally relates to a graphic contour extracting method, a pattern inspecting method, a program and a pattern inspecting system.
2. Description of the Prior Art
In a process of inspection in a semiconductor manufacturing process, image data of a pattern to be inspected are often acquired by an electron microscope, an optical microscope, a charge coupled device (CCD) or the like, to utilize contour information on the pattern to be inspected which is extracted on the basis of the image data. As contour information extracting methods, various methods have been put to practical use. For example, such methods include a method for setting a predetermined density value as a threshold value to define a portion corresponding to the threshold value as an edge when an acquired pattern image is a variable density image, a method for comparing an acquired pattern image with a closed curve graphic form serving as a reference, and a method for detecting a pattern edge by means of a two-dimensional filter, such as a Sobel filter.
Generally, when such a process is carried out, a region of interest (ROI) is assigned to a region of interest in an obtained image, and an edge extracting algorithm for executing any one of the above described various methods is executed in the interior of the assigned region to acquire a sequence of coordinate points of an edge corresponding to contour information to calculate geometric characteristic amounts, such as a line width, an area and a position of center of gravity, from data with respect to the obtained sequence of coordinate points.
As a shape of a boundary for defining an ROI region (an ROI boundary), a rectangle, an ellipse or a circle is often adopted for convenience of definition of the region. A method for assigning a rectangular ROI region is most generally carried out. An example of a method for adopting an elliptical ROI region is disclosed in e.g. Japanese Patent Laid-Open No. 2001-091231.
When the rectangular ROI boundary is adopted in the prior art, a pattern edge is searched in a direction parallel to any one of sides of an ROI region 62 as shown in, e.g., FIG. 27. Such a method is used when a pattern edge is substantially straight like a pattern P50 shown in the figure.
With respect to a pattern having a closed curved contour, an elliptical (or a circle) ROI boundary is set so as to surround a pattern edge of the pattern (P52) as shown by, e.g., an ROI boundary 64b in FIG. 28, and a pattern edge is searched in a direction of a radius vector.
However, in an image of a semiconductor pattern, the two-dimensional shape of a body serving as an object is more complicated. Therefore, in an inspecting method in the prior art, there are some cases where an edge searching direction is parallel to a pattern edge. For example, in the prior art, in the case of a pattern P2 shown in FIG. 29A, a pattern edge is locally parallel to an edge searching direction in a region Ep2 which includes an end of the pattern p2. In such a case, an edge point to be extracted has multi-values, so that there is a problem in that it is not possible to extract a proper edge position. Even with respect to a pattern having a closed curved contour, there may be regions Ep4, Ep6, Ep8 and Ep10 wherein pattern edges are parallel to edge searching directions (directions of radius vectors) as shown by a pattern P4 in FIG. 30A. In these cases, a tester must set a plurality of ROIs in accordance with the complexity of the pattern as shown by an ROI 68 in FIG. 29B and ROIs 74a through 74g in FIG. 30B, respectively, so that the costs required for inspection are increased. In particular, there are some cases where patterns to be inspected in fact have more complicated contour shapes as shown by patterns P6 and P8 in FIGS. 31 and 32, respectively. For example, with respect to the pattern P6 shown in FIG. 31, the edge searching direction locally corresponds to approximate directions of pattern edges at two portions (regions Ep12 and Ep14), so that there is a problem in that the tester fails in searching for edge positions in such portions. In the pattern P8 shown in FIG. 32, an elliptical ROI boundary 78b is set for searching edges in directions of its radius vectors. Therefore, the edge searching directions substantially corresponds to directions of pattern edges in regions Ep16 through Ep30, so that there is a problem in that the tester fails in searching for edge positions.
In addition, even if a pattern has a substantially straight pattern edge, when end portions of two patterns P10 and P12 face each other as shown in, e.g., FIG. 33, or when pattern edges of two close line patterns are perpendicular to each other as shown by patterns P14 and P18 in FIG. 34, there is a problem in that an edge searching direction substantially corresponds to directions of edges of a line pattern (P14) at two portions if search is carried out in a lateral direction on the figure.
Moreover, as shown by an example of a scanning electron microscope (SEM) image in FIG. 35, there are some cases where an OPC pattern called a serif is given to a part of a pattern on a reticle. In the case of a pattern P64 shown in this figure, it is not possible to detect edges in a contour portion parallel to an edge searching direction in, e.g., a region Ep32. There is also a problem in that a plurality of candidates of proposed edge points with respect to a single edge searching direction are detected in a region Ep34 in the figure. In addition, there are some cases where an edge is extracted in a direction which is not perpendicular to the contour of the pattern as shown in a region Ep36 in the figure. A density variation PF2 of the image in the edge searching direction in this case is shown in FIG. 36A. Furthermore, FIG. 36B shows the density variation PF4 of the image when edge searching is carried out in a direction substantially perpendicular to the contour of the pattern. As can be clearly seen from the comparison of both figures with each other, when the edge searching direction is not perpendicular to the contour of the pattern, the waveform of density variation is rendered broader, so that it is easy to include noises. That is, it can be seen that errors are apt to generate in edge detection.
In order to eliminate these problems, for example, the above described Japanese Patent Laid-Open No. 2001-091231 discloses a method for preparing a graphic form exhibiting characteristics of a pattern and for searching edges in a direction perpendicular to the graphic form to acquire contour data. However, it takes a lot of processing time to calculate searching directions for all of sequences of edge points. In addition, when the prepared graphic form exhibiting characteristics of the pattern includes many edges, there is a problem in that it is not possible to skillfully search edges due to the influence of noises which generate from the edges of the prepared graphic form.
Also in the case of the above described threshold method for extracting contour information on the basis of a threshold value, there are following problems in accordance with a pattern to be inspected. For example, if the maximum value (peak) of density in an ROI is set to be 100% and the minimum value (bottom) is set to be 0%, and if a position having a predetermined threshold value (e.g., 50%) is detected as an edge, the peak and bottom positions of a signal waveform in an edge searching direction are clear as shown by, e.g., a density variation (signal waveform) PF6 in FIG. 37A, in a pattern wherein an edge portion perpendicular to a substrate is formed. Therefore, if the ROI is set so as to include the peak and bottom, it is possible to stably detect an edge by the threshold method. However, in the case of a pattern having a taper or the like, there are some cases where the bottom position is not clear as shown by PF8 in FIG. 37B. Therefore, as shown in the comparison of ROI 84 with ROI 86 in FIG. 37B, if the position of an ROI boundary varies, the position of 0% is shifted, so that the position of the edge is shifted to cause a problem in that the result of measurement includes errors.
According to a first aspect of the present invention, there is provided a graphic contour extracting method comprising: acquiring an image of a graphic form to be inspected; defining an inspection region for the image of the graphic form to be inspected by an inspection graphic form including at least one of a circle, an ellipse, a rectangle, a first rectangular graphic form, a second rectangular graphic form and a closed curved graphic form, at least one end of the first rectangular graphic form being replaced with anyone of a semi-circle, a semi-ellipse and a parabola, at least one of four corners of the second rectangular graphic form being replaced with a xc2xc circle or a xc2xc ellipse, the closed curved graphic form being expressed by the following expression:                                           (                          x              -                              x                0                                      )                    4                          a          4                    +                                    (                          y              -                              y                0                                      )                    4                          b          4                      =    1    ,
and the inspection graphic form having an edge searching direction previously defined for at least one component thereof; and searching an edge of the graphic form to be inspected on the basis of the inspection graphic form to acquire contour information of the graphic form to be inspected.
According to a second aspect of the present invention, there is provided a graphic contour extracting method comprising: acquiring an image of a graphical form to be inspected; defining a potential function V for the image of the graphical form; calculating a first group of curves which are formed by connecting equal values with respect to values expressed by the potential function V; calculating a second group of curves which are substantially perpendicular to the first group of curves; and searching a contour of the graphical form along the second group of curves to acquire contour information of the graphical form.
According to a third aspect of the present invention, there is provided a graphic contour extracting method comprising: acquiring an image of a graphical form to be inspected, the image being constituted by pixels; preparing a polygonal line having a shape approximating the shape of the graphical form; determining an edge searching direction on the basis of the polygonal line; and analyzing a density distribution of the pixels of the image in the edge searching direction to detect coordinates of an edge point of the graphical form.
According to a fourth aspect of the present invention, there is provided a pattern inspecting method comprising: acquiring an image of a pattern to be inspected; defining an inspection region for the pattern by an inspection graphic form including at least one of a circle, an ellipse, a rectangle, a first rectangular graphic form, a second rectangular graphic form and a closed curved graphic form, at least one end of the first rectangular graphic form being replaced with anyone of a semi-circle, a semi-ellipse and a parabola, at least one of four corners of the second rectangular graphic form being replaced with a xc2xc circle or a xc2xc ellipse, the closed curved graphic form being expressed by the following expression:                                           (                          x              -                              x                0                                      )                    4                          a          4                    +                                    (                          y              -                              y                0                                      )                    4                          b          4                      =    1    ,
and the inspection graphic form having an edge searching direction previously defined for at least one component thereof; and searching an edge of the pattern on the basis of the inspection graphic form to acquire contour information of the pattern.
According to a fifth aspect of the present invention, there is provided a pattern inspecting method comprising: acquiring an image of a pattern to be inspected; defining a potential function V for the image of the pattern; calculating a first group of curves which are formed by connecting equal values with respect to values expressed by the potential function V; calculating a second group of curves which are substantially perpendicular to the first group of curves; and searching a contour of the pattern along the second group of curves to acquire contour information of the pattern.
According to a sixth aspect of the present invention, there is provided a pattern inspecting method comprising: acquiring an image of a pattern to be inspected, the image being constituted by pixels; preparing a polygonal line having a shape approximating the shape of the pattern; determining an edge searching direction on the basis of the polygonal line; and analyzing a density distribution of the pixels of the image in the edge searching direction to detect coordinates of an edge point of the pattern.
According to a seventh aspect of the present invention, there is provided a program for causing a computer to execute a graphic contour extracting method, the method comprising: acquiring an image of a graphic form to be inspected; defining an inspection region for the image of the graphic form to be inspected by an inspection graphic form including at least one of a circle, an ellipse, a rectangle, a first rectangular graphic form, a second rectangular graphic form and a closed curved graphic form, at least one end of the first rectangular graphic form being replaced with anyone of a semi-circle, a semi-ellipse and a parabola, at least one of four corners of the second rectangular graphic form being replaced with a xc2xc circle or a xc2xc ellipse, the closed curved graphic form being expressed by the following expression:                                           (                          x              -                              x                0                                      )                    4                          a          4                    +                                    (                          y              -                              y                0                                      )                    4                          b          4                      =    1    ,
and the inspection graphic form having an edge searching direction previously defined for at least one component thereof; and searching an edge of the graphic form to be inspected on the basis of the inspection graphic form to acquire contour information of the graphic form to be inspected.
According to an eighth aspect of the present invention, there is provided a program for causing a computer to execute a graphic contour extracting method, the method comprising: acquiring an image of a graphical form to be inspected; defining a potential function V for the image of the graphical form; calculating a first group of curves which are formed by connecting equal values with respect to values expressed by the potential function V; calculating a second group of curves which are substantially perpendicular to the first group of curves; and searching a contour of the graphical form along the second group of curves to acquire contour information of the graphical form.
According to a ninth aspect of the present invention, there is provided a program for causing a computer to execute a graphic contour extracting method, the method comprising: acquiring an image of a graphical form to be inspected., the image being constituted by pixels; preparing a polygonal line having a shape approximating the shape of the graphical form; determining an edge searching direction on the basis of the polygonal line; and analyzing a density distribution of the pixels of the image in the edge searching direction to detect coordinates of an edge point of the graphical form.
According to a tenth aspect of the present invention, there is provided a program for causing a computer to execute a pattern inspecting method, the method comprising: acquiring an image of a pattern to be inspected; defining an inspection region for the pattern by an inspection graphic form including at least one of a circle, an ellipse, a rectangle, a first rectangular graphic form, a second rectangular graphic form and a closed curved graphic form, at least one end of the first rectangular graphic form being replaced with any one of a semi-circle, a semi-ellipse and a parabola, at least one of four corners of the second rectangular graphic form being replaced with a xc2xc circle or a xc2xc ellipse, the closed curved graphic form being expressed by the following expression:                                           (                          x              -                              x                0                                      )                    4                          a          4                    +                                    (                          y              -                              y                0                                      )                    4                          b          4                      =    1    ,
and the inspection graphic form having an edge searching direction previously defined for at least one component thereof; and searching an edge of the pattern on the basis of the inspection graphic form to acquire contour information of the pattern.
According to an eleventh aspect of the present invention, there is provided a program for causing a computer to execute a pattern inspecting method, the method comprising: acquiring an image of a pattern to be inspected; defining a potential function V for the image of the pattern; calculating a first group of curves which are formed by connecting equal values with respect to values expressed by the potential function V; calculating a second group of curves which are substantially perpendicular to the first group of curves; and searching a contour of the pattern along the second group of curves to acquire contour information of the pattern.
According to a twelfth aspect of the present invention, there is provided a program for causing a computer to execute a pattern inspecting method, the method comprising: acquiring an image of a pattern to be inspected, the image being constituted by pixels; preparing a polygonal line having a shape approximating the shape of the pattern; determining an edge searching direction on the basis of the polygonal line; and analyzing a density distribution of the pixels of the image in the edge searching direction to detect coordinates of an edge point of the pattern.
According to a thirteenth aspect of the present invention, there is provided a pattern inspecting system comprising: an image acquiring part which acquires an image of a pattern to be inspected; an inspection region defining part which defines an inspection region for the pattern by preparing an inspection graphic form including at least one of a circle, an ellipse, a rectangle, a first rectangular graphic form, a second rectangular graphic form and a closed curved graphic form, at least one end of the first rectangular graphic form being replaced with any one of a semi-circle, a semi-ellipse and a parabola, at least one of four corners of the second rectangular graphic form being replaced with a xc2xc circle or a xc2xc ellipse, the closed curved graphic form being expressed by the following expression:                                           (                          x              -                              x                0                                      )                    4                          a          4                    +                                    (                          y              -                              y                0                                      )                    4                          b          4                      =    1    ,
and the inspection graphic form having an edge searching direction previously defined for at least one component thereof; and a contour extracting part which searches an edge of the pattern on the basis of the inspection graphic form to acquire contour information of the pattern.
According to a fourteenth aspect of the present invention, there is provided a pattern inspecting system comprising: an image acquiring part which acquires an image of a pattern to be inspected; a calculating part which defines a potential function V for the image of the pattern, calculates a first group of curves which are formed by connecting equal values with respect to values expressed by the potential function V, and calculates a second group of curves which are substantially perpendicular to the first group of curves; and a contour extracting part which searches a contour of the pattern along the second group of curves to acquire contour information of the pattern.
According to a fifteenth aspect of the present invention, there is provided a pattern inspecting system comprising: an image acquiring part which acquires an image of a pattern to be inspected, the image being constituted by pixels; a polygonal line preparing part which prepares a polygonal line having a shape approximating the shape of the pattern; an edge searching direction determining part which determines an edge searching direction on the basis of the polygonal line; and a contour extracting part which analyzes a density distribution of the pixels in the edge searching direction to detect coordinates of an edge point of the pattern.